1. Field of the Invention
The present invention relates to a simulation apparatus and a simulation method for simulating the intensity of an electromagnetic field etc. radiated from an electronic apparatus by using the moment method; more particularly, it relates to a simulation apparatus and a simulation method using the moment method with which the intensity of an electromagnetic field etc., of time domain can be simulated at a high speed.
Electronic apparatuses are restricted by society from radiating more than a certain level of undesired radio waves or noise. Countries are establishing tough regulations in this regard.
In order to satisfy such radio wave regulations, use is made of various countermeasures such as shielding technology and filtering technology etc. When adopting these countermeasures, it is necessary to develop simulation technology to enable simulation of the degree of reduction of the radio waves or noise in a quantitative manner.
Electronic apparatuses are also restricted by society from being affected by radio waves or noise radiated from other electronic apparatuses, which level is more than a certain level. Countries are also establishing tough regulations in this regard.
2. Description of the Related Art
So as to satisfy these radio wave regulations, it is necessary to develop simulation technology enabling analysis of the reasons why electronic apparatuses radiate undesired radio waves or noise and why electronic apparatuses malfunction due to radio waves or noise.
In order to develop the latter simulation technology, an electromagnetic field intensity calculation apparatus which can simulate the intensity of the electromagnetic field which changes in time becomes necessary. However, this type of electromagnetic field intensity calculation apparatus for simulating the intensity of the electromagnetic field which changes in time has not yet been put into practical use. The reason for this will be explained below.
The intensity of the electromagnetic field radiated from any shape of object can be easily calculated by using known theoretical equations if the current (electric current) and magnetic current flowing in each part of the object are known. These current and magnetic current can be theoretically obtained by solving Maxwell's electromagnetic equations under given boundary conditions.
As the method of solving this, there is the moment method. The moment method is one of the methods of solving integration equations derived from Maxwell's electromagnetic equations and the method calculates the current and magnetic current by dividing an object into small elements and therefore is able to handle any three-dimensionally shaped object. As a reference on the moment method, there is "H. N. Wang, J. H. Richmond, and M. C. Gilreath: "Sinusoidal reaction formulation for radiation and scattering from conducting surface", IEEE TRANSACTIONS ANTENNAS PROPAGATION. vol. AP-23, 1975".
On the other hand, to solve why an electronic apparatus radiates undesired radio wave or noise and why an electronic apparatus malfunctions due to a radio wave or noise, analysis by the time domain is necessary. This is because what most causes malfunctions of electronic apparatuses is pulse-like noise. Further, malfunctions of electronic apparatuses are frequently caused by abnormal operation of devices contained in the apparatus, such as ICs. It is necessary to observe these devices over time so as to confirm their abnormal operation.
Two useful methods for time domain analysis are the finite element method and finite difference method. Although time domain analysis is possible with the finite element method and finite difference method, it is difficult to deal with electronic apparatuses comprising a variety of structures such as transmission lines, cables, and housings.
This is because, in the finite element method and finite difference method, it is necessary to perform segmentation of the analyzed object and the three-dimensional space surrounding it. When performing fine segmentation for small parts such as the cable terminating portions, since the space surrounding the housing and cables is huge, the number of segmentations becomes enormous and ends up overload in capacity of internal memories of the computer. Conversely, when rough segmentation is performed for the cables, housing, and other structures, it becomes impossible to analyze the effect of the cable terminating portions which play an important role in the mechanism and also become large sources of undesired radio wave or noise.
Further, in the finite element method and finite difference method, the coordinate system used for the segmentation is generally the orthogonal coordinate system. However, the cable and cable terminating portions, which play an important role in mechanism, are comprised of cylindrical elements, while the housing of the apparatus may be of any shape. Due to this, there exists a difficult question of how to segment the analyzed object.
In this regard, the moment method is free from all such problems and is well suited for dealing with electronic apparatuses comprising a variety of structures such as transmission lines, cables, and housings.
This is because the moment method is a type of boundary element method and requires that only the boundary surface be segmented two-dimensionally. Further, the segmentation pitch can be determined considerably freely, so the small parts can be finely segmented and the cables and the housing can be roughly segmented, so a number of segmentations much smaller than with the finite element method and finite difference method is sufficient. Further, since any shape of segmentation can be used, the problem of how to perform the segmentation does not exist.
Therefore, it can be considered that a noise current, noise voltage and radiation intensities of electromagnetic field which change in time are simulated by using the moment method. Namely, when the wave source which changes in time is given, it can be considered to adopt a method in which, the wave source is transformed to the frequency domain, the radiation intensities of the electromagnetic field are simulated in the transformed frequency domain, and the simulated values are inversely transformed to the time domain.
However, this method also cannot be realized with the related art. This is because the moment method works, when the frequency is given, by calculating a mutual impedance, mutual admittance, and mutual reaction among mesh-like elements and using the calculated values, to solve simultaneous equations, but the time for calculation itself of the mutual impedance etc. is long and, at the same time, when transformed from the time domain to the frequency domain, a considerably large number of frequencies is required. Since it is necessary to calculate the mutual impedance etc. at respective frequencies, an enormous amount of processing time becomes necessary.
Namely, when calculating the intensity of radiation of an electromagnetic field by using the moment method, as will be explained later referring to the drawings, a very long time is taken for the calculation of each of the mutual impedance, mutual admittance, and mutual reaction. In addition, since the computation must be carried out at respective frequencies of the frequency domain, this computation cannot be done in a practical time.
More concretely speaking, the time taken to solve the simultaneous equations under the moment method is on the order of a few minutes in the case of a single frequency, but the time taken for computing the mutual impedance, mutual admittance, and mutual reaction becomes on the order of a few hours. Since the mutual impedance and so on must be computed at respective frequencies of the frequency domain, the calculation cannot be finished within a practical time frame.
Note that the mutual impedance shows the relationship between the electric field induced by current flowing in one element and the current flowing in another element. The mutual admittance shows the relationship between a magnetic field induced by a magnetic current passing through one element and the magnetic current passing through another element. The mutual reaction shows the relationship between the magnetic field (electric field) induced by a current (magnetic current) applied to one element and the magnetic current (current) applied to another element. A current flows through metal, while a current and magnetic current flow on the surface of a dielectric body.
As seen from the above explanation, at the present time, no practical electromagnetic field intensity calculation apparatus able to simulate the intensity of an electromagnetic field which changes in time has yet been developed which can analyze apparatuses including printed board, cables, and housings.